The concentration in SIgA/IgA, SIgM/IgM, and IgG did not differ between COVID-19 PCR, viral symptom, and Ctl-2018 groups (overall means ± SD: 1427 ± 521 μg/mL for SIgA/IgA, 3 ± 2 μg/mL for SIgM/IgM, and 10 ± 6 μg/mL for IgG). Here, CD40LG is linked to COVID-19.